How Belief Works is an ongoing series of articles on the psychology of belief that's best read in sequence, starting with A Note on the Term Belief.

As I stated in the previous article, belief involves a claim. For example, we may believe that killing is wrong or that David is vegetarian. And it might seem obvious why we believe what we believe: we believe claim X because we've assessed that X is true.

However, this apparent truism is actually false, because it’s fatally logically flawed. To understand why, consider first the distinction between the claims X and X is true.

Claim X versus the claim X is true

Compare these two sentences:

1. 1. It’s raining.

   2. The claim It’s raining is true.

2 can seem to be just a different wording of 1, and therefore to be making the same claim. However, 1 and 2 are actually making distinct claims that merely imply each other.

If two sentences are different wordings of the same claim, then, by definition, their content is the same. And if the content of two sentences is the same, then, by definition, neither sentence will refer to something that the other doesn’t refer to.

But whereas 2 refers to the claim It’s raining, 1 doesn’t. 1 makes, rather than refers to, this claim. That is, whereas 2 refers to a claim about the current weather, 1 refers to simply the current weather.

Also, 2, unlike 1, refers to the concept of truth, and thereby also to the relationship between the claim It’s raining and reality.

2 can be slightly reworded as follows:

The claim It’s raining is a true claim.

And it should now be even more apparent that 1 and 2 are making distinct claims that merely imply each other. That is: if it’s raining then the claim It’s raining is a true claim, and vice versa.

So 2 is merely implicitly making the claim that 1 is making.

2 can seem to be just a different wording of 1 because the claim made by 1 follows so obviously from the claim made by 2 that we can fail to notice the very basic logical step separating these claims.

The following two sentences are just different wordings of 2:

It’s true that it’s raining.

The truth is that it’s raining.

They might seem to be referring to simply the current weather, rather than to a claim about the current weather, and therefore to be just different wordings of 1.

However, unlike 1, they refer to the concept of truth. And this concept concerns a claim – specifically, a claim matching reality. The term true belief can either mean belief of a true claim – which is belief as in believing something – or a true claim that’s believed – which is belief as in something believed.

So when we state ‘It’s true that…’ or ‘The truth is that…’ we’re stating that the claim made by the subsequent words is a true claim. Therefore the above two sentences are actually both referring to the claim It’s raining. That is, they’re both stating that the claim It’s raining is a true claim, as 2 does, even though they don’t refer to the claim It’s raining as a claim, as 2 does.

The distinction between the claims made by 1 and 2 of course applies to any claim, X, and the claim X is true. Therefore claim X doesn’t in itself constitute the claim that X is true, and vice versa. Instead, each claim merely implies the other.

Belief X versus the belief X is true

Now consider our belief of the claims X and X is true.

Given that the claims made by sentences 1 and 2 are distinct claims that merely imply each other, our belief of them are, by definition, distinct beliefs that merely imply each other. That is, if we believe that it’s raining then we’d conclude that the claim It’s raining is a true claim. And, conversely, if we believe that the claim It’s raining is a true claim then we also believe that it’s raining.

But our belief of these two claims can seem to be the same belief because, again, the claims follow so obviously from each other that we can fail to notice the very basic logical step separating them.

The distinction between our belief of these two claims of course applies to our belief of any claim, X, and the claim X is true. Therefore believing X doesn’t in itself constitute believing that X is true, and vice versa. Instead, believing X merely implies that we’d conclude that X is true, and believing that X is true merely implies that we believe X.

The true relationship between belief and an assessment of truth

The distinction between believing claim X and believing that X is true implies a fatal logical flaw in the idea that we believe X because we’ve assessed that X is true. If believing X was dependent on us believing that X is true, then, given the distinction between these beliefs, believing that X is true would in turn be dependent on us believing that the claim X is true is true, and so on – which implies an infinite chain of belief formation. Belief formation would therefore be impossible.

And there’s a second fatal logical flaw in this theory of belief formation – one which reveals the true relationship between belief and an assessment of truth.

By definition, a claim is a true claim if, and only if, it matches reality. Therefore the only way to assess whether a claim is a true claim is to assess whether it matches reality. And the only way to assess whether a claim matches reality is to compare it with reality. However, when we compare a claim with reality we ultimately can only ever compare it with what we believe about the relevant aspect of reality at the moment of the comparison, even when that belief is based on the current content of our senses.

Therefore our assessment that the claim It’s raining is a true claim must be based on our belief that it’s raining. That is, this assessment must actually be preceded by our belief that it’s raining. Therefore our belief that it’s raining can’t ever be due to us assessing that the claim It’s raining is a true claim.

And this logic applies to the formation of any belief: our belief of claim X can’t ever be due to us assessing that X is true, because that assessment is always based on, and therefore preceded by, our belief of X.

However, the process of assessing the truth of X can lead to the formation of our belief of X, because this belief may only form during that process, the moment before we conclude that X is true.

It might be thought that our assessment that X is true is by definition an instance of believing something because we’ve assessed that it’s true. But this belief involves the claim X is true, and yet is formed via an assessment that X, not X is true, is true.

Potential objections

Objection 1

It might be objected that there’s one scenario in which we definitely believe claim X because we’ve assessed that X is true.

If we read or hear X, and we neither believed or disbelieved X immediately before doing so, and we completely trust X’s source on the subject of X, then we can assess that X is a true claim based on that trust, and this assessment will then immediately lead us to conclude X.

This sequence of events doesn’t imply the infinite chain of belief formation mentioned earlier, given that our belief that X is true is based on our trust of X’s source, and therefore isn’t dependent on us believing that the claim X is true is true.

Of course, not all of our beliefs follow from us reading or hearing the believed claim when we completely trust the claim’s source on the subject of the claim. Many of our beliefs follow instead from our generation of the believed claim via our reasoning. In the case of such beliefs that are about our surroundings or body, our reasoning is aided by our senses.

Indeed, in the above sequence of events our belief that X is true follows from our generation of the claim X is true via our reasoning, based on our trust of X’s source, rather than following from us reading or hearing the claim X is true.

Therefore the aim of this objection isn’t to show that we always believe X because we’ve assessed that X is true. Indeed, if it was, the objection wouldn’t provide a solution to the resulting problem of the infinite chain of belief formation.

But the objection doesn’t even succeed in its limited aim of showing that there’s one scenario in which we believe X because we’ve assessed that X is true, because it has two flaws.

First, in the above sequence of events our conclusion that X is a true claim actually doesn’t constitute an assessment that X is a true claim.

Again, by definition, a claim is a true claim if, and only if, it matches reality. Therefore the only way to genuinely assess whether a claim is a true claim is to assess whether it matches reality. And the only way to genuinely assess whether a claim matches reality is to compare it with reality – that is, compare it with what we believe about the relevant aspect of reality at the moment of the comparison, even when that belief is based on the current content of our senses.

Therefore if our conclusion that a claim is a true claim is based on simply a consideration of its source, and so not on a comparison of it with reality, then it’s based on an assessment of not its truth but that source. Therefore in the above sequence of events our belief of X is based on us concluding, but not assessing, that X is true.

The second flaw in this objection is that our complete trust of X’s source on the subject of X actually leads directly to us concluding X, rather than via concluding that X is a true claim.

Although that complete trust means, by definition, that we believe that all claims produced by the source on the subject of X can be believed to be true claims, this in turn means that we also believe that all such claims can be believed. Therefore upon reading or hearing X we can conclude X directly rather than via concluding that X is a true claim. And given that the former mental route to concluding X is shorter than the latter, we conclude X via the former route before we’ve had a chance to do so via the latter.

Objection 2

It might be objected that if our assessment that claim X is true was based on our belief of X, rather than the reverse, then our belief of X would lead us to always assess that X is true and that any contrary claim is false, and we’d therefore never change our belief, and yet we do change our beliefs.

However, this objection wrongly assumes that if we believe X then changing this belief is dependent on us assessing that X is a false claim and that a contrary claim is a true claim. Just as our belief of X can’t be due to our assessment that X is a true claim, because the reverse is true, so the subsequent formation of a contrary belief, and thus the end of our belief of X, can’t be due to us assessing that the contrary claim is a true claim and that X is a false claim, because the reverse will be true.

Also, as I mentioned earlier, the process of assessing the truth of X can lead to the formation of our belief of X, because this belief may only form during that process. Likewise, if we believe X and then assess the truth of both X and a contrary claim, we can change to believing the contrary claim during this process, and then assess that the contrary claim is a true claim and that X is a false claim. So believing X before assessing the truth of both X and a contrary claim doesn’t even mean that we’ll necessarily assess that X is a true claim and that the contrary claim is therefore false.

The origin and persistence of this false theory of belief formation

The origin and persistence of the idea that we believe claim X because we’ve assessed that X is true is likely due to the combination of the following factors:

• The claims X and X is true follow so obviously from each other that we can fail to notice the very basic logical step separating them, and therefore think that the two sentences making these claims are just different wordings of the same claim – and therefore in turn think that to believe X is to believe that X is true.

• If our belief of X formed during the process of assessing the truth of X, then that process was a critical part of the mental chain of events that led to our belief of X. And this fact can lead us to wrongly think that our belief of X is due to our assessment that X is true – especially given that our belief of X will have formed only the moment before we concluded that X is true.

• When we compare claim X with reality, in order to assess the truth of X, we can easily forget that we ultimately can only ever compare X with what we believe about the relevant aspect of reality at the moment of the comparison, even when our belief is based on the current content of our senses. Therefore when we assess that X is true we can wrongly think that we compared X with reality itself, rather than our belief about reality, and so only formed our belief of X upon forming that assessment.

• When we conclude that X is true based on our complete trust of X’s source on the subject of X, we can wrongly think both that this conclusion constitutes an assessment of truth, and that it led to our belief of X, even though our trust will have led directly to us concluding X.

So why do we believe what we believe?

There’s actually a third fatal logical flaw in the idea that we believe claim X because we’ve assessed that X is true.

We obviously can only begin to assess the truth of a claim after it has entered our mind, whether it does so upon us hearing it, reading it, recalling it, or generating it with our reasoning or imagination. But the entrance of a claim into our mind via our reasoning is a conclusion, which is by definition a belief. So we believe such a claim before we’ve had a chance to even begin to assess its truth.

The fact that a conclusion is by definition a belief can also seem to provide the answer to the question of why we believe what we believe: we believe claim X not because we’ve assessed that X is true, but because X was the product of our reasoning. Again, when we read or hear X we can conclude X based simply on our complete trust of X’s source on the subject of X.

Even the formation of beliefs about our surroundings or body via sensory perception requires at least some reasoning about the content of our perceptions.

Given that any belief involves a claim, a belief formed via perception involves a claim about the physical world, such as It’s raining. And the formation of any belief involves thinking the claim concerned. For example, the formation of the belief that it’s raining involves thinking 'It’s raining'.

But sensory perception is a distinct form of cognition from thinking and therefore believing. That is, the output of the perceptual process is simply our sensory experience of the physical world, which doesn’t in itself involve thinking claims about the physical world. For example, our vision of the scene in front of our eyes is simply our visual experience of that scene, and therefore doesn’t in itself involve thinking claims about the scene.

Such thoughts about our surroundings or body can instead be the product of our reasoning about the content of our perceptions. However, such reasoning is often so basic and therefore brief that the resulting belief can seem to be a direct product of the perceptual process.

The theory that we believe claim X because X was the product of our reasoning can seem true by definition and therefore unimpeachable. But so can the theory that we believe X because we’ve assessed that X is true. And, incredibly, even the former is fatally logically flawed.

As I'll explain in the next article, the answer to the question of why we believe what we believe is provided by a counterintuitive, and largely disregarded, theory of belief formation that was published over three centuries ago, and which has profound implications for human psychology and our lives.

Next article: How Beliefs Form

How Belief Works